If a display is a device for representing a thing seen by an eye like a real thing in a 2-D way, the lighting is an artificial device for generating light close to natural light. To this end, in the industry, methods capable of abundantly representing colors of things using natural light generated from the light of the sun are invented. Furthermore, as a color of light of the light of the sun in the middle of the day is different from that of light around evening, attempts to represent various color temperatures are being made even in artificial light sources. For example, efforts to increase R9 values indicative of a high Color Rendering Index (CRI), a color temperature, and the capability of a light source capable of well representing red are being made.
In the case of an LED, in general, a color temperature is controlled by coating an YAG fluorescent substance for changing blue into yellow on an element that emits blue by changing a concentration of the YAG fluorescent substance. If the concentration of the YAG fluorescent substance is low, white light having a high color temperature of a feeling of coolness is emitted. In contrast, if the concentration of the YAG fluorescent substance is high, white light having a low color temperature of a feeling of warmth is emitted. An R9 value, that is, a value indicating the degree that red inherent in a thing can be well represented, may be increased by adding a fluorescent substance for absorbing blue light and emitting red light instead of the YAG fluorescent substance.
A method used to fabricate a surface light source using LEDs includes a method of arraying small LED chips at the edge of a substrate that performs surface light emission (i.e., an edge type) and a method of placing several small LEDs on a light-emitting surface in a 2-D way and then adding a diffuser in order to cover the position of the LEDs (i.e., a direct type). In order for a surface light source, fabricated described above, to have a color control capability, LEDs that emit only red light or LEDs that emit only blue light are mixed and disposed. In such a case, a user can produce a low or high color temperature or various colors using the white surface light-emitting source.
In an OLED, unlike in the LED, the size of a unit element is relatively very large. In the case of a display using OLED technology, fine pixels of 1 mm or less are formed by the patterning of a substrate using lithography and the patterning of light-emitting substances, such as red, green, and blue, using a shadow mask, and the fine pixels are individually driven at the same time, thereby being capable of implementing various images. In contrast, if such methods are introduced in order to use OLEDs in the lighting, there is no practicality due to a very high price rise. For this reason, a relatively large surface light-emitting source that emits one kind of color, in particular, while light having a predetermined color temperature is fabricated. In general, an OLED has a size of 1×1 cm in width or height to 60×60 cm in width or height. Accordingly, unlike in the LED, in the OLED, a method of placing a plurality of light-emitting sources at the edge of a surface is used, or a method of forming one surface light-emitting source using a substrate itself because the OLED is large enough to be placed over a substrate formed of a surface so that it is not seen by an eye as in the direct type LED is used. Accordingly, a construction for producing the color control capability, such as that of the LED, is made difficult.
In the prior art, a method of sequentially stacking two elements over one substrate, pulling out intermediate electrodes from the elements separately, driving the intermediate electrodes individually, and performing color transform by controlling the intensity of light has been disclosed. However, only when the intermediate electrodes are transparent, two light-emitting colors placed over and under the intermediate electrodes can be mixed and discharged. To this end, thin metal having a relatively high permeability is used as the intermediate electrode. However, such a method may not becomes a practical method owing to a problem in that voltage rises due to an increase in the resistance of the intermediate electrode and a problem in that the intermediate electrodes have to be patterned in order to prevent a short problem occurring due to a direct and electrical connection between the upper and lower electrodes. Accordingly, a current lighting apparatus using an OLED panel is chiefly fabricated to produce a fixed white color.